Azeotropic Refrigerant Mixture R‑513A Separation Using Extractive Distillation with Ionic Liquids Entrainers

Hydrofluoroolefins (HFOs) are the next generation of refrigerants that have significantly lower global warming potential (GWP) and zero ozone-depleting potential (ODP) and will function as a replacement for hydrofluorocarbons (HFCs). During the transition to HFO refrigerants, a blend of HFC and HFO will be used to reduce the GWP and provide thermophysical properties that are suitable for use in replacing HFCs in existing equipment that may not be compatible or operating with the same performance with only HFOs. The formation of azeotropes in HFC/HFO blends poses a challenge when recycling and reclaiming the refrigerant. To address the problem of azeotropic mixture separation, a highly efficient separation method is required. Extractive distillation using an ionic liquid (IL) as an entrainer is proposed, offering effective separation of azeotropic mixtures. The effectiveness of ILs as an entrainer was determined by selectivity and high affinity toward one or more components of the mixture. The proper selection of the IL as an entrainer for a particular gas mixture is dictated by the purity of the products and the energy and cost of separation. Nine ILs were individually simulated in an equilibrium-based model to separate R-513A using ASPEN Plus to compare the impact of solvent choice on the separation cost. The ILs exhibited variations in overall heat duties, number of stages (N_T), operating pressure (P), solvent to feed ratio (S/F), and reflux ratio (RR). The best entrainer option for the separation of R-513A was found to be 1-ethyl-3-methylimidazolium acetate.